Ampaire is replacing the Cessna 337 Skymaster aft piston engine with an electric motor. The rear Continental IO-360 piston engine is replaced with an electric motor powered by a battery in a parallel hybrid configuration, optimising power output to reduce operating costs and pollution. The centerline thrust makes the 337 a useful testbed, allowing thrust differences with no yawing unlike a conventional twin-engine aircraft. Ampaire is marketing the EEL to government departments and private owners while undisclosed commercial operators already placed orders. Manufactured between 1965 and 1982, there is in-service fleet of 2,500 of the six-seat aircraft. EEL refers to the original 337 designation, with the characters reversed. Ampaire wants to offer multiple single and twin-engined aircraft, powered by its proprietary electric-propulsion system.
Development
By January 2019, Ampaire planned to fly the prototype on Hawaiian Mokulele Airlines commuter routes operated with Cessna Caravans. Seven other airlines are interested by Caravan or Twin Otter conversions: Seattle’s Kenmore Air, Tropic Air of Belize, Puerto Rico-based Vieques Air Link, Southern Airways Express of Memphis, Tennessee, Guernsey’s Aurigny and Star Marianas Air, based in the Northern Mariana Islands, as well as Norway. Test flights will take place on a route over 15 minutes between Kahului Airport in Central Maui and Hana Airport on the East side. The hybrid prototype held its first public test flight on June 6, 2019, before scheduled service planned for 2021. Later that month, Personal Airline Exchange became the launch customer for the electric EEL modified six-seat Skymaster, to be certified in 2021, with an order for 50 plus 50 options. US start-up PAX is an on-demand per-seat charter offering point-to-point service competing with driving, is connecting small airports to bypass hubs and congested roads. PAX will acquire two Cessna 337s, sourced and refurbished by Ampaire, to start commercial operations in early 2020 in southern California before a nationwide introduction, with their original engines. A second prototype should be flight tested from the end of 2019, with the battery not inside the cabin but attached to the aircraft belly. With this second prototype, Hawaiian regional carrier Mokulele Airlines will experiment connecting Maui airports. It will be limited to a pilot and two non-paying passengers, below its six-seat capacity, and Mokulele will provide hangar space, parts, pilots and maintenance. A similar pilot project is supported by Vieques Air Link, a regional airline in Puerto Rico. The certification and service entry of the EEL is planned for 2021. By October 2019, the configuration was swapped with the piston engine in the back and the electric system forward, with batteries installed in a belly pod, to be flight tested by Mokulele Airlines in the first quarter of 2020.
